title: Magnetic resonance image intensity ratio, a normalized measure to enable interpatient comparability of left atrial fibrosis.
abstract: BACKGROUND
  The measurement of late gadolinium-enhanced magnetic resonance imaging (LGE-MRI) intensity in arbitrary units limits the objectivity of thresholds for focal scar detection and interpatient comparisons of scar burden.
  
  
  OBJECTIVE
  To develop and validate a normalized measure, the image intensity ratio (IIR), for the assessment of left atrial (LA) scar on LGE-MRI.
  
  
  METHODS
  Electrocardiogram- and respiratory-gated 1.5 Tesla LGE-MRI was performed in 75 patients (75% men; 62 ± 8 years) before atrial fibrillation ablation. The local IIR was defined as LA myocardial signal intensity for each of the 20 sectors on contiguous axial image planes divided by the mean LA blood pool image intensity. Intracardiac point-by-point sampled electroanatomic map points were coregistered with the corresponding image sectors.
  
  
  RESULTS
  The average bipolar voltage for all 8153 electroanatomic map points was 0.9 ± 1.1 mV. In a mixed effects model accounting for within patient clustering, and adjusting for age, LA volume, mass, body mass index, sex, CHA2DS2-VASc score, atrial fibrillation type, history of previous ablations, and contrast delay time, each unit increase in local IIR was associated with 91.3% decrease in bipolar LA voltage (P < .001). Local IIR thresholds of >0.97 and >1.61 corresponded to bipolar voltage <0.5 and <0.1 mV, respectively.
  
  
  CONCLUSIONS
  Normalization of LGE-MRI intensity by the mean blood pool intensity results in a metric that is closely associated with intracardiac voltage as a surrogate of atrial fibrosis.
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Irfan M
authors.initials: IM
authors.lastname: Khurram
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Roy
authors.initials: R
authors.lastname: Beinart
authors.affiliation: Department of Biostatistics, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Vadim
authors.initials: V
authors.lastname: Zipunnikov
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Jane
authors.initials: J
authors.lastname: Dewire
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Hirad
authors.initials: H
authors.lastname: Yarmohammadi
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Sasaki
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: David D
authors.initials: DD
authors.lastname: Spragg
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Marine
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Ronald D
authors.initials: RD
authors.lastname: Berger
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland; Department of Radiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Henry R
authors.initials: HR
authors.lastname: Halperin
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Hugh
authors.initials: H
authors.lastname: Calkins
authors.affiliation: Department of Radiology, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Stefan L
authors.initials: SL
authors.lastname: Zimmerman
authors.affiliation: Department of Medicine/Cardiology, Johns Hopkins University, Baltimore, Maryland. Electronic address: snazarian@jhmi.edu.
authors.forename: Saman
authors.initials: S
authors.lastname: Nazarian
mesh_terms: D001281:Atrial Fibrillation / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D018780:Body Surface Potential Mapping; D009202:Cardiomyopathies / Q000150:complications / Q000175:diagnosis*; D003937:Diagnosis, Differential; D004562:Electrocardiography; D005260:Female; D005355:Fibrosis / Q000473:pathology; D005500:Follow-Up Studies; D006325:Heart Atria / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000473:pathology*; D015203:Reproducibility of Results; D012189:Retrospective Studies
keywords: AF; Atrial fibrillation; EAM; Electroanatomic mapping; IIR; LA; LGE; Late gadolinium–enhanced magnetic resonance imaging; MRI; PV; Scar; atrial fibrillation; electroanatomic map; image intensity ratio; late gadolinium enhancement; left atrial; magnetic resonance imaging; pulmonary vein